Method of drying yeast



Patented Sept. 20, 1927.

UNITED STATES.

PATENT OFFICE.

ARNOLD K. BALLS, OF PHILADELPHIA, PENNSYLVANIA;

mnrnon on name user.

No Drawing. Application filed'neoeniber 13, 1923, Serial No. 680,528.Renewed August 16, 1927.

This invention relates to methods of dryin yeast.

he development of methods for drying yeast without impairing the bakingstrength or the keeping qualities of the yeast has been a matter of muchinvestigation, and various methods for drying yeast have been developed.As a general rule, the ordinary yeast races sold for baking in thiscountry and submitting it to a rapid drying operation at a relativelyhigh temperature.

This method differs from those heretofore proposed in that theconditions for the most rapid possible drying have been studied, andboth by adding to the yeast an inert substance to increase its porosityand by work ing at greatly raised temperatures and with very dry air,the time of drying has been reduced to from one-third to one-sixth ofthat heretofore considered necessary. The advantage of sucha rapidprocess is obvious,

5 not only from the standpoint of increased technical production, butalso by avoiding the necessity of keeping moist yeast for hours in theapparatus at temperatures favorable to autolysis, growth of infections,

and general weakening of the yeast.

The use of vacuum drying apparatus is unnecessary, and the inst-antdrying of the 'yeast by spray driers is harmful to the product.

The yeast is grown in the usual manner, separated and compressed, andabout 10 per cent of its weight of substantially pure cellulose freefrom soluble impurities and white or light in color, is then added tothe yeast.

The yeast is then finely divided and placed in layers of from one-fourthto three-fourths of an inch in thickness in a tray drier and submittedto the drying operation. In drying the yeast, a starting temperature offrom 20 to 30 C. is employed and prefer- "fibre by digesting it withdilute acids if any .ably a temperature of 25 0., and a depresdepressionare maintained throughout the process and suflicient volume of air maybe employed to complete the drying in from 3 to 4 hours.

Either of the drying methods may be employed. The alternative processset forth requires considerable more equipment to produce the proper airconditions in the presence of moist yeast than the condition set forthin the preferred form of the process.

The maximum hygrometric depressions attained are those of practicallydry air. There is an apparent advantage aside from the time saved, to begained by employing the heavy currents of air necessary to produce theseresults.

The purified cellulose em loyed is repared from bran, rice polis ings orlimt starch is present. I have found that a solution of 1 per centhydrochloric acid may be employed for removing the starch. The celluloseis then mixed and stirred with a small amount of bleaching powder,sodium hypochlorite or chlorine, washed, and dried.

Yeast dried according to either of the methods set forth when previouslymixed with cellulose as described, will keep its baking strengthunimpaired for at least one month at ordinary room temperatures, ascompared with the baking strength of an equivalent quantity of freshyeast. By keeping the dried yeast at temperatures below 20 0., theoriginal baking strength may be kept for many months. If the yeast iskept below 5 no deterioration occurs within a period of two years. Bykeeping the yeast at temperatures below 0 G., I have found that thebaking qualities are even improved at the end of two or three months.

A suitable amount of calcium sulfate,

. from 2 per cent to 5 per cent by weight, may

be added to increase the baking strengh of the yeast.

The maximum temperature of 40 employed in the drying operation may beslightly varied and a temperature of about 43 C. may be employed. Whennearly dry, the yeast can stand higher temperatures for fairly shortperiods and a temperature (4550) approaching the thermal death C pointof wet yeast, has been employed without impairing the yeast.

The use of the cellulose filler greatly facilitates drying andapparently adds to the keeping quality of the dried yeast by adsorbingcarbon dioxid, butyric acid, acetic acid, and the like, which aregradually liberated from dry yeast on storage.

The filler also presents an economic advantage in that the amount oftime necessary to complete the drying operation is materially reduced.When the drying operation is performed according to the first methoddescribed, the apparatus is very simple and inexpensive. No vacuum unitis employed and no dehumidifying agent is necessary.

While I have described in detailthe preferred practice of my process, itis to be understood that the details of procedure may be widely varied,without departing from the spirit of the invention or the scope of thesubjoined claims.

I claim:

1. The herein described product comprising a mixture of dried yeast andcellulose.

2. The hereindescribed product comprising a mixture of dried yeast andsubstantially 30cper cent by weight of cellulose.

3. he herein described process of drying yeast which comprises addingcellulose thereto and subjecting the mixture to a drying action.

4. The process of drying yeast which comprises adding cellulose to ayeast and dryin it at a temperature between 20 C. and 40 5. The processof drying yeast which comprises adding cellulose to a yeast and dryingit at a temperature between 20 C. and 40 in an atmosphere having adepression between 10 and 18.

. 6. The process of drying yeast which comprises adding cellulose to ayeast and drying it with an initial temperature of from 20 C. to 30 C.in an atmosphere having a depression of substantially 10, increasing thetemperature to substantially a0", and the depression to 15 to 18.

7. The process of drying yeast which comprises adding cellulose to ayeast and dry ing it for a period of 6 to 8 hours in an atmospherehaving an initial temperature of substantially 25 C. and a depressionof.

substantially 10, and increasing the temperature to substantially 40 C.and the depression to from 15 to 18.

8. The process of drying yeast which comprises adding cellulose anddrying With practically dry air at a temperature of 35 to 40 C. and insufiicient volume to reduce the moisture content to approximately 10 percent in about three hours.

9. The'process of dryin yeast which com-' prises adding cellulose tiereto, submitting the mixture to treatment with heated air until dry.and controlling the temperature and l"

